Film-tape synchronization system

ABSTRACT

In the disclosed system, a control circuit drives a projector by comparing the speed of the projector with the rate of clock signals from a pulse generator. When the projector reaches a start index on the film a detector disables the pulse generator so that the control circuit stops the projector. At the same time the detector connects the control circuit to the tape which has clock signals recorded along with the sound. As soon as the tape reaches the point where the sound and clock signals begin the control circuit restarts the projector and keeps it running in synchronism with the tape.

United States Patent [1 1 Ogiso et al. 1 May 15, 1973 [54] F ILM-TAPESYN CHRONIZATION [56] References Cited Y TEM S S UNITED STATES PATENTS[75] Inventors: Mitsutoshi Ogiso, Kawaski-shi,

Kanagawa ken; Takashi Rani 3,620,609 11/197] John ..352/17 ku, Tokyo;Kiyoshi Takahashi, Ku-

a Primar Examiner-Samuel S. Matthews t h ,T k ll H Y m ac l Shl 0 a apanAssistant ExaminerMichael L. Gellner [73] Assignee: Canon KabushlklKalsha, I Atmmey David Tore et aL Shimomaruko, Ota-ku, Tokyo, Japan 57]ABSTRACT Filed! J y 1 In the disclosed system, a control circuit drivesa pro- [211 APPL No: 165 999 jector by comparing the speed of theprojector with the rate of clock signals from a pulse generator. Whenthe projector reaches a start index on the film a detec- [30] ForeignApplication Priority Data tor disables the pulse generator so that thecontrol circuit stops the projector. At the same time the detector July24, 1970 Japan ..45/64859 connects the control circuit to the tape whichhas clock signals recorded along with the sound. As soon [i] as the tapereaches the point where the Sound and 15 16 17 clock signals begin thecontrol circuit restarts the pro- 1 o earc jector and keeps it runningin synchronism with the tape.

14 Claims, 3 Drawing Figures owl Signal from another recorder 4 V. U..wfim Signal to another recorder PATENIEDIIIYI 51m I 3,733,117

SHEET 1 [IF 2 O OSCILLATOR CONTROL m- P PROJECTOR H 2 2 1 SI (c) I 25%Pc 3 F ,mzcoao HEAD 7 \45? T\ *flSiQZ TAPE RECORDER I I k i I AME ERASEi s g I S i, W

1 Reference Pulse Signal M LA LIL (Sigi) I 1| 1 I I I I I I I I I PulseSignal From Pro ector o I I I (SigZ) l I i i' I I 5 I I I i I I I I I iI l I i I I o-+ I I i g Power Distribution Supplied to Motor ofProjector o v INVENTOR Minutes oi. 0 1150 7347: 8 76 Ii -am. Afiyosfii7a4'a m8fie BY 7 2 M ATTORNE PATENTEDHAY 1 51875 3,733,117

SHEET 2 [1F 2 Signal from another recorder FIG.2

Tr C7 D3 4 Signal to another recorder M INVENTOR c'isatosfii O 5 WQS'AZ33% BY L Z fa/ mS/u Mau 9 771% ATTORNE BACKGROUND OF THE INVENTION Thepresent invention relates to a synchronized playback system forsynchronously reproducing a recorded film such as a cinematographic filmand a recorded tape using a synchronization signal, and moreparticularly relates to a system for synchronously preproducing the filmand the tape precisely by phase comparison of reproduced synchronizationsignal which has been recorded on a magnetic tape at a time ofphotographing and so on with a signal corresponding to a film speed atthe time of projection of the film.

In a conventional synchronization playback system, the tape speed of atape recorder is detected as a rotational speed and the film speed of afilm projector is detected as a rotational speed, and these detectedrotational speeds are compared with each other and their differenceactuates a switch to short a electro-magnetic field of a motor of theprojector for synchronization. However, in this type of conventionalsystem, high degree of skill is required for the synchronization andadjustment, and such system fail to give sufficiently precisesynchronization during play-back of the system. Furthermore severalfilm-tape synchronization systems using synchronization signal have beenproposed, but they have been found insufficient in their performance andreliability and operational easiness.

An object of the present invention is to furnish a filmtapesynchronization system which overcomes the above defects of theconventional systemsv SUMMARY OF THE INVENTION According to the presentinvention, a train of pulse signals recorded together with sound signalson a tape is detected from the tape to turn on a driving motor of theprojector by means of a thyristor, and a train of pulse signals from thethe projector and corresponding to the film speed is detected to turnoff the driving motor by means of a transistor which is connected inseries with the thyristor.

Further according to the present invention, a circuit for converting atrain of pulse signals of opposite polarity from a tape recorder to atrain of signals of the same polarity is provided to detect the train ofsignals of the same polarity through the converting circuit, and anoutput therefrom turns on a driving motor at the side of the projectorby its output and a train of pulse signal from the side of the projectorand corresponding to the film is detected to turn off the driving motorby the output. As the present invention is provided with an automaticelectronic control in the synchronization system, error in speeddetection and mechanical delay in speed control are avoided.

The present invention shall be described in reference to the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustratingthe film-tape synchronization system of the present invention.

FIG. 2 is a circuit diagram showing one embodiment of the film-tapesynchronization system according to the present invention.

FIG. 3 is a graph illustrating power distribution (c) supplied to theprojector with that (a) of reference pulse signals and that (b) of apulse signal from the projector.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. 1, which is ablock diagram of the system in which after-recording of sound iseffected during the projection of a film and projection of a film iseffected during play-back of a tape recorder, P is a projector, C is acontrolling circuit, F is a feed-back path, 0 is an oscillator, AR is anamplifier, T is a tape recorder, B is a synchronization box providedwith a recording head AH for synchronization signal and a reproducinghead of the signal and an eraser circuit E and so on. Thesynchronization box may be set in the tape recorder T. The variouselements of the synchronization system shown in FIG. 1 may be integratedinto a single unit as a sound projector or may be provided separately. Achangeover switch S switches the system from its condition of recordingsynchronization signals shown in FIG. 1 to its reproducing condition ofthe synchronization signal. By the changing over of the switch 8,, theoutput signal of the oscillator O is cut off and a reproduced output ofthe synchronization signal recorded in the synchronization box is put inthe controlling circuit C through the amplifier AR. The switch 8, alsoserves to bring back the reproducing condition to the recordingcondition.

A sensing circuit S is provided for starting the tape at the time of thestart of the film so as to match the start point of the recorded tapewith the start point of the recorded film. For this purpose, at thestart point of the film is provided a notch or opening or an signalframe for producing a start signal to start the delivery of a referenceoutput pulse signal of the tape to the controlling circuit C. Thismatching operation is carried out under the reproducing condition of thesystem.

For assuring this matching operation, the recording must be started atthe time of the start of projection for the after recording.

Next explanation will be made on one example of using the presentinventive system.

The present system is used for recording and reproducing sound signalslip synchronized with a cine film previously photographed. The switch Sis connected to a terminal 1 as shown in FIG. 1. In this state, lipsyn-' chronized sounds are produced during projection of the cine filmpreviously photographed. The sounds are applied to the amplifyingcircuit AH of the synchronization box B together with the referenceoutput pulses from the oscillator 0 through the amplifier AR from theterminal 2, and recorded on the sound track of the tape of the taperecorder T.

Then for reproducing the sounds, the switch S is connected to theterminal 3, and when the tape recorder T and the projector P areactuated, the sound signal recorded in the tape recorder T is reproducedby an additional unit (not shown) connected to the terminal 4 throughthe amplifying circuit AH. The reference output pulse signal recorded onthe tape is amplified by the amplifier AR and applied to the controlcircuit C through the switch S connected to the terminal 3. In thecontrol circuit C, the reference output signal is compared with anoutput signal corresponding to the film speed of the projector P andapplied through the feed-back path F. Thus the control circuit Csupplies the projector P with power in proportion to the phasedifference between these two output signals and controls the rotationalspeed of a driving motor of the projector P to synchronize the tape withthe film.

Next referring to FIG. 2 in which same references indicate same elementsas in FIG. 1, the oscillator O for producing the reference pulse signalin order to obtain a constant speed of the film speed at the projectorside comprises a double base diode U, resistors R R R R R and R acapacitor C and switches S S S and 8,. When the potential e of a timeconstant circuit composed of the capacitor C, and normally the resistorR and R becomes larger than the potential e, determined by the resistorsR and R the path between the anode of the double base diode U and thecathode of the diode U becomes conductive and the charge across thecapacitor C, is discharged through the resistor R,, and the capacitor C,reaches a residual charges in which no further discharge occurs andbecomes ready to recharge. In this way charging and discharging acrossthe capacitor C, is repeated to maintain oscillation in theoscillations. The switch 8;, controls the oscillator of the oscillatorO, and the switch S is associated with a relay coil R, in the sensingcircuit S.

The switch 8, serves to change the oscillation frequency to onecorresponding to that produced by the resistor R and the capacitor C,from the normal oscillation frequency. The switch 8,, serves to changethe oscillation frequency from the normal frequency to a frequencycorresponding to the resistors R R and R and the capacitor C,. Theswitches S and 8,, are respectively associated with the switches S andS,,. Thus a fine adjustment for the synchronization is attained by theoperation of these switches S S S and 8,, when the projector deviatesfrom the reference pulse signal by a few frames. This adjustment is veryuseful for finely adjusted reproduction.

The switch S, is also associated with the relay coil R and the switch Sand S, are associated with the switches 8 and S The control circuit Ccomprises a thyristor SR,, transistors Tr, and Tr a diode D,, resistorsR-,, R R R,,,, R,,, R and R,;,, capacitors C and C The control circuit Ccontrols the speed of the projector. The gate of the thyristor SR,receives a reference pulse signal Sig, as shown in FIG. 3 from theoscillator O or the magnetic tape and so on, and thereby the thyristorSR, is turned on. The transistor Tr, is biased in a normally conductivestate by the transistor Tr The transistor Tr, is also biased in anormally conductive state by the resistors R, and R,,. The reed switch Sprovided at the projector side, is connected in parallel with theresistor R,;,.

The reed switch S senses the rotational speed of the projector P andbecomes conductive to produce a differentiated negative pulse signalSig, as shown in FIG. 3 through the capacitor C and the resistor R,,.The differentiated negative signal Sig renders the transistors Tr, andTr, non-conductive for a moment to turn off the thyristor SR,.

The control circuit C controls a rectangularly distributed power signalPc supplied to the motor M in proportion to the phase difference betweenthe reference pulse signal Sig, and the negative pulse signal Sig: whoserepetition rate is in proportion to the speed of the projector. In casethe phase difference between the reference pulse signal Sig, and thenegative pulse signal Sig, fed back from the projector is large, namelyin case the speed of the projector is lower than the speed correspondingto the reference signal, the power supply to the motor of the projectorincreases and the motor of the projector is accelerated to attain thestandard speed. On the contrary, in case the phase difference betweenthe reference pulse signal Sig, and the negative pulse signal Sig, fedback from the projector is small, namely in case the speed of theprojector is higher than that corresponding to the reference pulsesignal, the

power P -supplied to the motor of the projector decreases and the motorof the projector is decelerated to attain the standard speed. When thevoltage supplied to the motor of the projector becomes large and thespeed of the motor of the projector becomes high, the phase differencebetween the reference pulse signal Sig, and the pulse signal Sig fromthe projector becomes small. Thus the power Pc supplied to the motor ismaintained constant to assure a constant speed of the motor of theprojector.

While when the voltage becomes small, the phase difference between thereference pulse signal Sig, and the pulse signal Sig, from the projectorbecomes large, and thereby the power Pc supplied to the motor of theprojector is maintained constant. Further, even when there is torquevariation use to such as film leads, the projector speed is controlledto a speed corresponding to the reference pulse signal Sig,.

The sensing circuit S comprises a transistor Tr a thyristor SR a relaycoil RL, a photocell Pc, a diode D resistors R R R and R and switches Sand S,,. The switch 8, is associated with the switches 5, and 8, and theswitch 8,, is associated with the switch S3.

The notch or opening or a signal frame provided at a prescribed positionof the film is detected by the photocell P0 and the output of thephotocell P0 is amplified by the transistor Tr, to turn on the thyristorSR and actuate the relay coil RL and keep it in its actuated state. Therelay coil RL turns on the switch S to stop the oscillation of theoscillator O and the relay coil RL actuates the driving means of thetape recorder. The actuation of the driving means is effected bypinching action of a pinch roller to a capstan as usually done by theclosing action of a main switch of the driving circuit of the drivingmotor for the tape recorder.

The switch 8, is provided for changing over the controlling circuit Cfrom the oscillator O to the read amplifier AR.

The eraser circuit E comprises an eraser head HE for erasing therecorded signal of the tape and the switch 8, The head amplifyingcircuit AH reproduces the reference pulse signal recorded on themagnetic tape etc., and comprises a magnetic head Hp, both for recordingand playback, a transistor Tr resistors R R, R and R capacitors C and Cand switches S,,. The magnetic head Hp both for recording and play-backserves as a recording head by changing over the switch 8,, for recordingthe reference pulse signal onto the magnetic tape.

The amplifier circuit AR amplifies the signal from the head amplifiercircuit AH or converts the reference pulse signal from another recorderinto a signal suitable to the controlling circuit C. This amplifyingcircuit AR comprises transistors Tr, and Tr,,, diodes D D and Dresistors R R R R R R and R and capacitors C C C and C The signal fromthe amplifying circuit AH is directly amplified and supplied to thecontrolling circuit C through the switch S As the controlling circuit Crequires positive pulse signal, in case the reference pulse signal inputto the terminal 2 from the another recorder is positive pulse, the pulsesignal is supplied to the base of the transistor Tr through thecapacitor C and the diode D and the output a from the transistor Tr issupplied to the controlling circuit C.

In case the reference pulse signal input to the terminal 2 from theanother recorder is negative pulse, the pulse is supplied to the base ofthe transistor Tr through the diode D and the phase inversion is carriedout and thereby the inverted output from the transistor Tr is suppliedto the controlling circuit C through the transistor Tr The resistor Rserves to decay the signal potential from the another recorder so as tomatch the output level from the transistor Tr with that for the otheroutput with no phase inversion. When the driving circuit for driving themotor of the projector synchronously is actuated together with theswitches S and S the switch S is maintained on while the switch S isturned off. When the driving circuit for driving the motor of theprojector synchronously is not actuated, the switch S is off and theswitch S is on, and the speed of the projector P is selected freely bymeans of a variable resistor VR E is a power source for the system and Eis a power source for driving the motor of the projector.

The operation of the circuit shown inFIG. 2 is summerized for two cases.

1. When the reference pulse signal during the same period as the periodrequired for the projection of the film is recorded previously from theoscillator 0 into the tape of the tape recorder T.

In this case, the period required for projection of the film ispreviously measured. The reference pulse signal Sig is recorded from theoscillator O for the period on the recording tape etc. of the taperecorder T from the magnetic head Hp for recording and reproducing inthe amplifier AI-I, or on the recording tape etc. of the anotherrecorder from the output terminal 4 for the another recorder. Next thestart position of a scene of the film is made ready for starting theprojection by means of the notch or opening or signal frame, and thestart position of the tape etc. recorded in this way is also preset forits starting. At this instance, when the initial setting is performed.The notch or opening or signal frame of the scene strictly correspondsto the first pulse signal of the reference pulse signal on the tape.

When the film is set in the projector P and the oscillator 0 starts itsoscillation, the reference pulse signal Sig is delivered to thecontrolling circuit C to start the projector P, and the signal Sig inproportion to the seed of the projector is fed back to the controllingcircuit C through the feedback path F by the reed switch S set in theprojector P, and thereby the projector P is caused to move at a constantspeed by the reference pulse signal Sig,. When the next notch or openingor signal fame passes the front of the photocell Po, the output of thephotocell is amplified by the transistor Tr;, to actuate the thyristorSR and thereby to actuate the relay coil RL. The switch S associatedwith the relay coil RL becomes on at this instance, and the oscillator 0stops its oscillation to stop the projector P. In this way the film inthe projector is set precisely at a next start position of the nextscene. The switch 8, also associated with the relay coil RL is changedover from the oscillator O to the amplifier AR. At this moment, when thetape recorder T is started, the reference pulse signal previouslyrecorded is reproduced by means of the head Hp and supplied to thecontrolling circuit C the amplifier circuit through the convertingcircuit on the amplifier circuit AR the diode D or D etc. when the firstpulse of the reference pulse signal from the tape recorder T or from theanother recorder reaches the controlling circuit C, the circuit C startits actuation, and at the same time the projector P starts itsactuation. In this case the tape speed corresponding to the referencepulse signal recorded on the magnetic tape or the recording material ofthe another recorder corresponds to the speed of the projector, namelythe film speedis l to 1 onto mapping of the tape speed. Therefore, whensound required for each cut or each frame of the film is recorded on theportion other than the recorded track for the reference pulse signal isrecorded on the magnetic tape of the tape recorder T or on the recordingmaterial of the another recorder, the sound strictly corresponding toeach frame or each cut of the film is recorded. By reproducing the filmand the magnetic tape provided in the above way, the projected image andthe reproduced sound are precisely synchronized.

2. In case of using a magnetic tape etc. having no recorded signal.

In this case, by a notch or opening or signal frame is provided at thestart portion of the scene of the film and the magnetic tape is set inthe tape recorder T or the another recorder. As previously described,the switch S of the oscillator O is made off for actuation of theoscillator O for actuation of the projector P. In this way the notch oropening or signal frame is set at its start position as describedbefore. In this state, the tape recorder T or the another recorder isset for its recording and the recording is started. And then theswitches S S and S are changed over to the recording side of thereference pulse signal to turn on the switch 8, and thereby to connectthe switch S to the oscillator 0. Thus the head Hp is set for recordingand ready for recording and at the same time the relay coil RL kept atits actuation state by the thyristor SR is reset or dienergized by theswitching off of the switch S and the switch 5., associated with therelay coil RL is made off to produce the reference pulse signal Sig fromthe oscillator 0. And the change over switch 8, also associated with therelay coil RL is changed over from the amplifier circuit to theoscillator O to supply the reference pulse signal Sig to the controllingcircuit C and also to the head Hp. In this way the signal correspondingto the film is recorded on the magnetic tape. During this recording,sound corresponding to frames or cuts of the film is effectivelyrecorded on portions other than the portion having recorded pulsesignal.

In this case also a strict reproduction is attained in a one-to-one ontomapping manner as described previously. The foregoing description hasbeen made on reproduction of the cinematographic film by means of acinematographic projector. However, the present invention is not limitedto the above, but is also useful for reproducing synchronously recordedsound with recorded film during projector, and recording the soundcorresponding to the object to be photographed at the very time ofphotographying by controlling a cinematographic camera through thecontrolling circuit C at a constant speed in stead of controlling theprojector by the reference pulse signal from the oscillator or recordedon the tape at the time of shooting.

What is claimed is:

l. A system for recording and reproducing audiovisual information bysynchronizing a projector for projecting images recorded on a film withrecorder means for recording and reproducing sound signals, comprisingelectric signal generator means for selectively generating electricalsignals which are regular and independent of the feed of the film, saidgenerator means having switching means for enabling and disabling saidgenerator means, said film having a start index, a detector coupled tosaid switching means for detecting the start index and causing saidswitching means to disable said generator means after detecting thestart index, driving means for feeding the film of the projector, andcontrol means for actuating and controlling said driving means, saiddriving means having a driving circuit, said control means having aswitching circuit connected to the driving circuit of said drivingmeans, said switching circuit means being connected electrically to theoutput of said generator means.

2. A system as in claim 1, wherein said reproducing means has a tape forrecording sound signals on which synchronizing signals are recorded in apredetermined relationship with the sound signals, said reproducingmeans including a detector for detecting synchronizing signals recordedon the tape of the reproducing means, said output means selectivelyconnected to said switching circuit means.

3. A system as in claim 1, wherein said switching circuit means includesa pair of switching elements connected in series, one of said elementsbeing made conductive by the output of said generator means, the otherof said elements being made conductive synchronously by the film feed ofthe projector.

4. A system as in claim 1, wherein said switching circuit means includesa pair of switching circuit elements connected in series, adifferentiation circuit responsive to the film feed of the projector,said differentiation circuit opening and closing one of said elements,the other of said elements being open and closed by the output of saidgenerator means.

5. A system for synchronizing movement of film in a projector with asound track wherein the film has a starting index and the sound trackhas a signal portion, said system comprising control means responsive totiming signals and to the speed of the film movement in the projectorfor actuating the projector at a speed depending on the relationshipbetween the rate of the timing signals and the speed of the projectorand for stopping the projector in the absence of timing signals, timingsignal generator means for generating timing signals, switch means forcoupling said generator means to said control means so that said controlmeans actuates the projector and moves the film, electrical means forcarrying timing signals from the signal portion of the sound track,sensing means responsive to the appearance of the index on the film forcausing said switch means to decouple said control means from saidgenerator means and to couple the control means to said electrical meansafter the sensing means senses the index so as to end the timing signalsto the control means until timing signals arrive on said electricalmeans.

6. A system as in claim 5, further comprising electrical means forconnecting said generator means to the signal portion of the sound trackso as to record the timing signals on the signal portion of the soundtrack.

7. A system as in claim 5, wherein said generator means includes asecond switch means responsive to said sensing means for suppressing thetiming signals in said generator means after said sensing means hassensed the index.

8. A system as in claim 7, further comprising electrical means forconnecting said generator means to the signal portion of the sound trackso as to record the timing signals on the signal portion of the soundtrack.

9. A system as in claim 5, wherein said sound track is in the form of atape, ad further comprising tape recording means couplable to saidgenerator means for recording the timing signals from said generatormeans onto the sound track while sound is being recorded on the soundtrack, said tape recorder means being connectable to said electricalmeans for reproducing the timing signals and applying them to saidcontrol means through said electrical means when said control means isconnected to said electrical means by said switch means.

10. A system for presenting audiovisual information so that a projectorfor projecting images recorded on a film is synchronized with a taperecorder for producing sound signals, comprising electric signalgenerator means for selectively generating electrical signals which areregular and independent of the feed of the film, driving means forfeeding the film in the projector, control means for actuating andcontrolling said driving means, said control means having an electricalsource and switching circuit means connected between the driving meansand the electrical source, the film having a start index, detector meansfor detecting a start index carried on the film, reproducing means forreproducing the synchronizing signals recorded in a certain positionalrelationship with the sound signals on the tape of the tape recorder,and switch means for selectively connecting said switching circuit meansto one of said reproducing means in said generator means, said switchmeans connecting said switching circuit means to said generator meansbefore said detecting means detects the start index and connecting saidswitching circuit means to said reproducing means after said detectormeans senses said start index.

11. A system as in claim 10, wherein said generator means includes aswitch for enabling and disabling said generator means, said switchbeing connected to said detector for disabling said generator means whensaid detector detects the start index.

12. A system as in claim 10, wherein said switching circuit meansincludes a switch member responsive to the speed of the film,differentiation circuit means connected to said switch member, and asecond switch member connected to said driving means and renderedconductive by the output of one electrode of said differentiationcircuit.

13. A system as in claim 12, wherein said switching circuit meansincludes a third switching member connected with the second switchingmember in series with the second switching member, said third switchingmember being rendered conductive by the output of said generator means.

14. A system as in claim 13, wherein said second switching member is atransistor and said third switching member is a thyristor.

1. A system for recording and reproducing audiovisual information bysynchronizing a projector for projecting images recorded on a film withrecorder means for recording and reproducing sound signals, comprisingelectric signal generator means for selecTively generating electricalsignals which are regular and independent of the feed of the film, saidgenerator means having switching means for enabling and disabling saidgenerator means, said film having a start index, a detector coupled tosaid switching means for detecting the start index and causing saidswitching means to disable said generator means after detecting thestart index, driving means for feeding the film of the projector, andcontrol means for actuating and controlling said driving means, saiddriving means having a driving circuit, said control means having aswitching circuit connected to the driving circuit of said drivingmeans, said switching circuit means being connected electrically to theoutput of said generator means.
 2. A system as in claim 1, wherein saidreproducing means has a tape for recording sound signals on whichsynchronizing signals are recorded in a predetermined relationship withthe sound signals, said reproducing means including a detector fordetecting synchronizing signals recorded on the tape of the reproducingmeans, said output means selectively connected to said switching circuitmeans.
 3. A system as in claim 1, wherein said switching circuit meansincludes a pair of switching elements connected in series, one of saidelements being made conductive by the output of said generator means,the other of said elements being made conductive synchronously by thefilm feed of the projector.
 4. A system as in claim 1, wherein saidswitching circuit means includes a pair of switching circuit elementsconnected in series, a differentiation circuit responsive to the filmfeed of the projector, said differentiation circuit opening and closingone of said elements, the other of said elements being open and closedby the output of said generator means.
 5. A system for synchronizingmovement of film in a projector with a sound track wherein the film hasa starting index and the sound track has a signal portion, said systemcomprising control means responsive to timing signals and to the speedof the film movement in the projector for actuating the projector at aspeed depending on the relationship between the rate of the timingsignals and the speed of the projector and for stopping the projector inthe absence of timing signals, timing signal generator means forgenerating timing signals, switch means for coupling said generatormeans to said control means so that said control means actuates theprojector and moves the film, electrical means for carrying timingsignals from the signal portion of the sound track, sensing meansresponsive to the appearance of the index on the film for causing saidswitch means to decouple said control means from said generator meansand to couple the control means to said electrical means after thesensing means senses the index so as to end the timing signals to thecontrol means until timing signals arrive on said electrical means.
 6. Asystem as in claim 5, further comprising electrical means for connectingsaid generator means to the signal portion of the sound track so as torecord the timing signals on the signal portion of the sound track.
 7. Asystem as in claim 5, wherein said generator means includes a secondswitch means responsive to said sensing means for suppressing the timingsignals in said generator means after said sensing means has sensed theindex.
 8. A system as in claim 7, further comprising electrical meansfor connecting said generator means to the signal portion of the soundtrack so as to record the timing signals on the signal portion of thesound track.
 9. A system as in claim 5, wherein said sound track is inthe form of a tape, ad further comprising tape recording means couplableto said generator means for recording the timing signals from saidgenerator means onto the sound track while sound is being recorded onthe sound track, said tape recorder means being connectable to saidelectrical means for reproducing the timing signals and applying them tosaId control means through said electrical means when said control meansis connected to said electrical means by said switch means.
 10. A systemfor presenting audiovisual information so that a projector forprojecting images recorded on a film is synchronized with a taperecorder for producing sound signals, comprising electric signalgenerator means for selectively generating electrical signals which areregular and independent of the feed of the film, driving means forfeeding the film in the projector, control means for actuating andcontrolling said driving means, said control means having an electricalsource and switching circuit means connected between the driving meansand the electrical source, the film having a start index, detector meansfor detecting a start index carried on the film, reproducing means forreproducing the synchronizing signals recorded in a certain positionalrelationship with the sound signals on the tape of the tape recorder,and switch means for selectively connecting said switching circuit meansto one of said reproducing means in said generator means, said switchmeans connecting said switching circuit means to said generator meansbefore said detecting means detects the start index and connecting saidswitching circuit means to said reproducing means after said detectormeans senses said start index.
 11. A system as in claim 10, wherein saidgenerator means includes a switch for enabling and disabling saidgenerator means, said switch being connected to said detector fordisabling said generator means when said detector detects the startindex.
 12. A system as in claim 10, wherein said switching circuit meansincludes a switch member responsive to the speed of the film,differentiation circuit means connected to said switch member, and asecond switch member connected to said driving means and renderedconductive by the output of one electrode of said differentiationcircuit.
 13. A system as in claim 12, wherein said switching circuitmeans includes a third switching member connected with the secondswitching member in series with the second switching member, said thirdswitching member being rendered conductive by the output of saidgenerator means.
 14. A system as in claim 13, wherein said secondswitching member is a transistor and said third switching member is athyristor.